Heat sink for tubular conveyor rolls

ABSTRACT

Reducing warping of tubular rolls employed in conveying sheet material at elevated temperatures. A liquid or gaseous medium is maintained within the interior of the rolls to act as a heat sink for equalizing the wall temperature circumferentially around and longitudinally along the rolls, thereby minimizing warping due to differentials in temperature.

United States Patent 1191 King HEAT SINK FOR TUBULAR CONVEYOR ROLLS Inventor: Roger P. King, Waterville, Ohio Libby-Owens-Ford Company, Toledo, Ohio Filed: July 19, 1971 Appl. No.: 163,585

Assignee:

US. Cl 65/356, 65/118, 65/245 Int. Cl C03b 29/04 Field of Search 65/356, 245, 118,

References Cited UNITED STATES PATENTS 1,754,826 Hitchcock 65/356 X 1 Dec. 18, 1973 5/1925 Evans 65/356 X 10/1921 Cox 1/1932 Drake...

2/1932 Fox 65/356 X Primary Examiner--Arthur D. Kellogg Attorney-Elmer L. Collins et a1.

ABSTRACT Reducing warping of tubular rolls employed in conveying sheet material at elevated temperatures. A liquid or gaseous medium is maintained within the interior of the rolls to act as a heat sink for equalizing the wall temperature circumferentially around and longitudinally along the rolls, thereby minimizing warping due to differentials in temperature 7 Claims, 3 Drawing Figures HEAT SINK FOR TUBULAR CONVEYOR ROLLS BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates broadly to the conveying of sheet material, and more particularly to rolls used in the conveying of the continuous sheet or ribbon of glass from a facility where it is produced, through an annealing lehr, to a capping area where it is separated into individual blanks for subsequent processing.

2. Description of the Prior Art One form of more or less conventional annealing lehr is illustrated and described in U. S. Pat. No. 3,469,964, issued Sept. 30, 1969, to James T. Zellers, Jr. As explained therein, following its formation from a mass of molten glass contained within a tank furnace, a continuous sheet or ribbon of glass is carried through an elongated annealing lehr on a series of horizontally aligned rolls for gradual cooling. Within the enclosed portion of the annealing lehr, heat is supplied as by gas-fired burners whereby the temperature of the ribbon is allowed to gradually decrease according to a predetermined pattern as it moves through the lehr, until it reaches a level at which it can safely exit from the enclosed portion and continue along the horizontal path for cooling to room temperature in the ambient atmosphere.

In the initial stages of the annealing lehr, the ribbon may be at a temperature on the order of 1,100 to 1,200 F., and for carrying the ribbon in this region chrome plated steel or stainless steel rolls are preferred. At subsequent stages of the annealing process, where the ribbon has cooled somewhat, metallic rolls covered with a heat resistant material such as asbestos have conventionally been employed. However, rolls of chrome plated steel are preferred over asbestos covered rolls in this area because of their durability and superior surface quality. Such chrome plated rolls sometimes have a tendency to bow or warp during use due to creation of unequal temperatures around their periphery. If the warping becomes pronounced, it tends to become self-perpetuating. Thus, as the warped roll rotates, the portion bowed convexly will contact the heated ribbon while the opposite or concavely bowed portion will not do so because of the supporting rolls at either side. Heat will be conducted to the portion which periodically engages the relatively hot ribbon, while the opposite portion will not be heated to a similar extent. AS a result, the temperature differential around the roll periphery, and hence the warping, is increased. This, in turn, tends to increase the temperature differential until a stable condition of unequal temperatures is reached.

If the amount by which the roll runs out as it rotates is great enough, that is, if it deviates from true axial alignment by a sufiicient amount, it will cause the ribbon to be periodically lifted off the adjacent rolls on either side. This, of course, creates temperature differentials in the adjacent rolls and they also warp. In actual practice, it has been found that warping in one roll will induce warping in the adjacent rolls on either side thereof which is 180 out of phase with the intermediate roll. This follows, of course, since the regions of higher temperature will be created in the adjacent rolls where they are in contact with the ribbon and the regions of cooler temperature will result where the ribbon is raised out of contact therewith by the high portion of the intermediate roll.

It will thus be apparent that one warped roll can adversely affect the rolls over a considerable span of the lehr system. Severely warped rolls have been found to run out by nearly one-half inch. Such warping not only adversely affects the operation of instruments used in this region to check the quality of the glass ribbon, such as optical devices for measuring its thickness, but also has been found to actually damage the surface of the ribbon.

SUMMARY OF THE INVENTION In accordance with the present invention, a liquid or gaseous medium is introduced into the interior of the lehr rolls. The medium acts as a heat sink within the rolls to prevent formation of and even out existing temperature differentials around the wall as the rolls r0- tate. Existing warpage due to uneven peripheral temperatures is thus substantially reduced and, since the temperature tends to equalize circumferentially around and longitudinally along the rolls, they do not warp through extended use.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings, wherein like numerals refer to like parts throughout:

FIG. 1 is a longitudinal side view, partially in vertical section, of an annealing and conveying apparatus embodying the invention;

FIG. 2 is a plan view, partially in section, of the apparatus and;

FIG. 3 is a longitudinal sectional view through a typical roll of the invention and taken substantially along line 3-3 of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now more particularly to the drawings, there is illustrated in FIG. 1 a typical annealing lehr for a continuous ribbon of glass. In the illustrated apparatus, there is shown generally at 10 an annealing lehr comprised of an enclosed section 11 and an open section 12. A continuous glass ribbon 13 produced by suitable apparatus such as shown in the aforementioned U. S. Pat. No. 3,469,964, is carried through the enclosed portion and along the open section of the lehr on a series of aligned rolls 14 which are suitably driven in a conventional manner (not shown).

The ambient atmosphere circulates beneath the rolls in the open section of the lehr so that they are subjected to a substantial temperature differential. In the enclosed portion, the temperature is substantially uniform around any given roll. Thus, the problem with which the present invention is concerned occurs primarily in the open section of the lehr, and only the exit end of the enclosed section 11 has been illustrated for purposes of describing the invention. It will be understood, however, that the principles of the invention are applicable to rolls at any location in the annealing process where warping occurs due to temperature differentials around or along the rolls, and that while the invention is described with reference to an annealing lehr for flat glass, it is generally applicable to conveying of any type of sheet material or any products at elevated temperatures.

The enclosed portion 11 of the lehr includes a roof l5, floor l6, opposite side walls 17, and an exit end wall 18. The ribbon 13 emerges from the enclosed section 11 of the lehr through an opening 19 in the end wall 18. Suitable heaters (not shown) are provided within the enclosed section to maintain the necessary temperature pattern so that the ribbon will be gradually cooled down to the appropriate level at the exit point. The ribbon is generally at a temperature on the order of 350 F. to 400 F. at this point, and is then allowed to gradually cool down to atmospheric temperature as it traverses the open section 12. A partition 20 is provided over the open section of the lehr within the lehr building to reduce convection currents moving therealong due to the temperature differential between the opposite ends of the open section.

An electronic optical thickness gauge such as disclosed closed in U. S. Pat. No. 3,591,293 issued July 6, 1971 to Robert E. Maltby et al., illustrated generally at 21, may be positioned over the ribbon to continually monitor its thickness. The operation of such optical instruments is dependent upon the ribbon remaining a fixed distance from the scanning mechanism. Warping of the rolls l4 therebeneath, whereby the ribbon is caused to fluctuate vertically, is thus particularly troublesome in that it causes erroneous and unreliable thickness readings.

In accordance with the present invention, warping in the rolls 14 is substantially eliminated, or at least reduced to the point of insignificance, by introducing a liquid or gaseous medium to the interior of the rolls to act as a heat sink for equalizing the temperature around and along the roll. To this end as illustrated in FIG. 3, the hollow cylindrical roll 14 is closed at the ends as by plates 22 forming a closed chamber 23 therein. A filler plug 24 may be threaded into an opening 25 in one of the end plates so as to provide access for admitting the heat sink medium to the chamber 23. Shafts 26 may be provided at the ends for joumaling and driving the rolls in a suitable manner, or they may be mounted for driven rotational movement in any other suitable manner conventional in the art. In rolls of the type illustrated, the shafts 26 may be hollow and the heat sink medium may also be admitted through one of the shafts to the chamber 23. The bodies of such rolls in a conventional annealing lehr are on the order of 14 feet in length and have an inside diameter of about I 1 inches, so that they have an internal volume of about 9.24 cubic feet or 69.16 gallons.

Any liquid which is stable at the temperatures encountered and which does not adversely affect the rolls as by corrosive attack thereon, may be employed in practicing the invention. Ordinary water has been found to perform very well in the rolls at the cooler end of the lehr where the temperature does not exceed its boiling point. In fact, with open-ended rolls having a surface temperature considerably above the boiling point of water, on the order of 450 F. to 500 F., very dramatic reductions in roll warp have been achieved by dripping water onto the interior surface from a pipe (not shown) inserted through the end thereof. The water droplets are immediately converted to steam and the steam serves to equalize the temperature around the roll. In one trial, for example, a roll operating at a surface temperature of 480 F., had a warp or run-out of 0. 102 inch. By dripping water into the roll at the rate of 2 gallons per hour for a period of IO minutes, the

warp was decreased to 0.005 inch, the amount of deviation measured with the roll at atmospheric temperature prior to the trial.

Continuous insertion of water to form steam within the rolls may not be practicable in many instances, and thus it is preferred to use a high-temperature heat transfer medium of the type known as Dowtherm A, made by the Dow Chemical Company of Midland, Mich., in the rolls operating at the higher temperatures. This particular heat transfer medium, which is the eutectic mixture of diphenyl and diphenyl oxide, has a boiling point of 494.8 F., and is useable up to a temperature of 750 F. The first roll outside the enclosed portion 12 of the lehr, which operates at the highest temperature, normally has a maximum temperature below 365 F. so that the Dowtherm A or equivalent high temperature heat transfer medium is suitable for use in any of these rolls where warping is a problem. Of course, in any of the rolls operating at a temperature at which it can be employed in the liquid state, water is the preferred medium from an economic standpoint.

Warping may occur to varying degrees throughout the open section 12 of the lehr due to the combined effect of the temperature of the glass ribbon and the temperature of the ambient atmosphere surrounding the rolls. However, it has been found that the tendency to warp to an appreciable extent is greatest in the first 12 or 15 rolls following the closed section 11, with the most severe warping occurring in the vicinity of and immediately after the partition 20.

The amount by which the warping or run-out is reduced by the invention is generally proportional to the volume of heat transfer medium within the roll acting as a heat sink, up to the point where run-out attributable to temperature differential is substantially eliminated. By way of example, in an operating lehr on a float glass furnace, the second roll preceding the partition 20 had a maximum surface temperature at the glass ribbon of 245 F. and a run-out of 0.303 inch. Five gallons of Dowtherm A were inserted through the opening 25 to form a liquid heat sink 27 (FIG. 3) in the lower portion of the roll chamber 23. After operating conditions stabilized, the run-out was reduced to 0.145 inch. The roll immediately preceding the partition 20, that is, the roll next to the above-discussed roll, had a run-out of 0.324 inch. Fifteen gallons of Dowtherm A were inserted as a heat sink 27 and, after operating conditions stabilized, the run-out was reduced to 0.010 inch. The sixth roll following the partition had a maximum surface temperature at the glass ribbon of about 200 F. and a run-out of 0.301 inch. Twenty gallons of water were inserted as a heat sink 27 so that the roll was less than about one-third filled and, after operating conditions became stabilized, the run-out was reduced to 0.004 inch.

It is to be understood that the forms of the invention herewith shown and described are to be taken as illustrative embodiments only of the same, and that various changes in the shape, size and arrangement of parts may be resorted to without departing from the spirit of the invention.

I claim:

1. ln apparatus for conveying a continuous ribbon of material at an elevated temperature along a predetermined path through an atmosphere at a temperature substantially lower than that of said ribbon, including a plurality of spaced tubular rolls upon which said ribbon is supported and means for driving said rolls to advance said ribbon along said path, the improvement comprising a liquid heat exchange medium thermally isolated within and partially filling the hollow interior of at least one of said tubular rolls in a zone where said ribbon is at said elevated temperature for exchanging heat with the wall of said roll to reduce the temperature differential in said wall as said roll rotates.

2. Apparatus for conveying a continuous ribbon of material as claimed in claim 1, wherein said liquid heat exchange medium is a body of a high temperature heat transfer liquid partially filling said hollow interior.

3. Apparatus for conveying a continuous ribbon of material as claimed in claim 1, in which said liquid heat exchange medium is a body of water partially filling said hollow interior.

4. In a method of reducing warping of a tubular roll employed in conveying a continuous ribbon of material at an elevated temperature through an atmosphere at a temperature substantially lower than that of said ribbon, the improvement comprising continuously directing a vaporizable liquid against the interior wall of said roll while said wall is at a temperature above the vaporization temperature of said liquid at a rate so as to vaporize all of said liquid and thereby maintain a body of fluid within the hollow interior of said roll for exchanging heat with the wall thereof, whereby any temperature differentials circumferentially around and longitudinally along the wall of said roll are reduced as said roll rotates.

5. A method of reducing warping of a tubular roll as claimed in claim 4, wherein water is continuously dripped onto said wall within said roll to maintain said fluid body.

6. ln apparatus for conveying a continuous ribbon of material at an elevated temperature along a predetermined path through an atmosphere at a temperature substantially lower than that of said ribbon, including a plurality of spaced tubular rolls upon which said ribbon is supported and means for driving said rolls to advance said ribbon along said path, the improvement comprising a fluid heat exchanging medium within the hollow interior of at least one of said tubular rolls for exchanging heat with the wall of said roll to reduce the temperature differential in said wall as said roll rotates, said one roll being open at one of its ends and including a pipe extending into the interior of said roll from the open end, means supplying a vaporizable liquid to said pipe, and means in said pipe allowing said liquid to drip onto the interior wall of said one roll, said wall being at a temperature above the vaporizing point of said liquid so that all of said liquid vaporizes as it drips onto said wall to fill said hollow interior and form said heat exchange medium.

7. In a method of reducing warping in a series of tubular rolls employed in conveying a continuous ribbon of glass at an elevated temperature through an atmosphere at a temperature substantially lower than that of said ribbon wherein warping of one of said rolls induces warping in the adjacent rolls on either side thereof which is out of phase with said one roll, the improvement comprising containing a body of liquid heat exchange medium within the hollow interior of said one roll, said heat exchange medium filling not more than about one-third of said hollow interior, and substantially thermally isolating said heat exchange medium within said one roll, said medium exchanging heat with the wall of said one roll as said one roll rotates to reduce the temperature differential in said wall whereby warping is reduced in said one roll and consequently in said adjacent rolls on either side thereof. 

1. In apparatus for conveying a continuous ribbon of material at an elevated temperature along a predetermined path through an atmosphere at a temperature substantially lower than that of said ribbon, including a plurality of spaced tubular rolls upon which said ribbon is supported and means for driving said rolls to advance said ribbon along said path, the improvement comprising a liquid heat exchange medium thermally isolated within and partially filling the hollow interior of at least one of said tubular rolls in a zone where said ribbon is at said elevated temperature for exchanging heat with the wall of said roll to reduce the temperature differential in said wall as said roll rotates.
 2. Apparatus for conveying a continuous ribbon of material as claimed in claim 1, wherein said liquid heat exchange medium is a body of a high temperature heat transfer liquid partially filling said hollow interior.
 3. Apparatus for conveying a continuous ribbon of material as claimed in claim 1, in which said liquid heat exchange medium is a body of water partially filling said hollow interior.
 4. In a method of reducing warping of a tubular roll employed in conveying a continuous ribbon of material at an elevated temperature through an atmosphere at a temperature substantially lower than that of said ribbon, the improvement comprising continuously directing a vaporizable liquid against the interior wall of said roll while said wall is at a temperature above the vaporization temperature of said liquid at a rate so as to vaporize all of said liquid and thereby maintain a body of fluid within the hollow interior of said roll for exchanging heat with the wall thereof, whereby any temperature differentials circumferentially around and longitudinally along the wall of said roll are reduced as said roll rotates.
 5. A method of reducing warping of a tubular roll as claimed in claim 4, wherein water is continuously dripped onto said wall within said roll to maintain said fluid body.
 6. In apparatus for conveying a continuous ribbon of material at an elevated temperature along a predetermined path through an atmosphere at a temperature substantially lower than that of said ribbon, including a plurality of spaced tubular rolls upon which said ribbon is supported and means for driving said rolls to advance said ribbon along said path, the improvement comprising a fluid heat exchanging medium within the hollow interior of at least one of said tubular rolls for exchanging heat with the wall of said roll to reduce the temperature differential in said wall as said roll rotates, said one roll being open at one of its ends and including a pipe extending into the interior of said roll from the open end, means supplying a vaporizable liquid to said pipe, and means in said pipe allowing said liquid to drip onto the interior wall of said one roll, said wall being at a temperature above the vaporizing point of said liquid so that all of said liquid vaporizes as it drips onto said wall to fill said hollow interior and form said heat exchange medium.
 7. In a method of reducing warping in a series of tubular rolls employed in conveying a continuous ribbon of glass at an elevated temperature through an atmosphere at a temperature substantially lower than that of said ribbon wherein warping of one of said rolls induces warping in the adjacent rolls on either side thereof which is 180* out of phase with said one roll, the improvement comprising containing a body of liquid heat exchange medium within the hollow interior of said one roll, said heat exchange medium filling not more than about one-third of said hollow interior, and substantially thermally isolating said heat exchange medium within said one roll, said medium exchanging heat with the wall of said one roll as said one roll rotates to reduce the temperature differential in said wall whereby warping is reduced in said one roll and consequently in said adjacent rolls on either side thereof. 